It is useful for diagnosing or detecting a disease process to perform a histologic or cytologic examination of a tissue cell sample using a light microscope. This requires that a tissue (cellular material) sample must first be retrieved from the patient, and then processed for microscopic examination. A number of minimally invasive techniques are available for retrieving and collecting cell samples from a patient, e.g., by using a fine needle aspiration biopsy, or by brushing body cavity surfaces accessible through minimally invasive endoscopic techniques. A variety of cell sample processing techniques are also known, such as the Cytospin® technique and the Thin-prep® technique, for depositing cellular materials and tissue fragments directly onto a microscope slide. Another technique, commonly referred to as a cell block preparation, immobilizes cellular materials and/or small tissue fragments within a solid support structure, typically paraffin. Thin sections of the cell block are then cut with a microtome and mounted onto a microscope slide for examination.
U.S. Pat. No. 6,913,921 discloses and describes methods and apparatus for cell block preparation, including providing a tissue collection cassette that serves a dual function of capturing cellular sample matter and providing a fluid pathway through which the cell processing and embedding reagents can flow. The cellular sample material is provided in an aqueous solution or a liquid cell preservative, which is passed through the tissue cassette across a filter that traps the cells and tissue fragments. A reagent flow pathway is configured to sequentially pass embedding reagents (alcohol, xylene, eosin stain) and liquefied paraffin through the tissue cassette and the cell sample already deposited on the filter. Once the paraffin is cooled, the filter is peeled away, leaving a paraffin “disk” protruding from the tissue cassette, with embedded cellular matter positioned at the end of the disk in a plane at which a tissue section can be cut using a standard microtome for microscope examination.
While representing an improvement over the then-state of the art for cell block preparation, the methods and apparatus disclosed in the '921 patent remain labor intensive, requiring manual operation and supervision, in particular, for determining when a sufficient quantity of cellular material has been gathered on the filter. Further, the cell sample fluid “pathway” (tubing and sample port) must be replaced following each use to avoid contamination of subsequent samples, and the filter-to-cassette connection relies on a relatively thick o-ring in order to create a sufficient length of paraffin cell block for later microtome slicing.